While testing the Panasonic GH3 camera, I took a series of nine identical pictures using the Lumix X 12-35mm f/2.8 lens in the high speed drive mode, with electronic shutter. They all came out fine, except for one single image, which came out without the pincushion in-camera geometric distortion correction. It also has some corrupted parts in the upper part of the image.
Here is one picture which came out ok, and the one out of nine which came out wrong:
I opened the JPEG file in several image processing programs to verify that the mistake was in the file, not in the editing client.
The RAW image file still came out fine, so this is not a big issue. I wouldn't recommend to avoid the camera because of this finding. It is probably normal that new cameras need some firmware upgrade to behave better. My camera has the original 1.0 firmware.
I later tried to take another long series of images, and they all came out just fine.
To verify that the corrupted image indeed has pincushion distortion, I have superimposed the edges from the JPEG image (in red) on the edges from the RAW image (in blue):
We see that the JPEG image has pincushion distortion, while the image based on the RAW file has the correct rectilinear appearance. If the camera worked well, both images should have the same geometric properties.